Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 231152 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 752 AM EDT THU APR 23 2015 .SYNOPSIS... A DEEP UPPER LEVEL LOW PRESSURE SYSTEM NORTH OF THE GREAT LAKES WILL KEEP TEMPERATURES ON THE COOL SIDE FOR THE MID ATLANTIC THROUGH THE REMAINDER OF THE WORKWEEK. HIGH PRESSURE BUILDING IN FROM THE WEST WILL MAINTAIN A TIGHTENED PRESSURE GRADIENT ACROSS THE REGION...RESULTING IN CONTINUED GUSTY NORTHWEST WINDS FOR TODAY. FOR THE WEEKEND...ANOTHER UPPER-LEVEL DISTURBANCE WILL BRING SHOWERS TO THE REGION...ALONG WITH CONTINUED COOL TEMPERATURES. && .NEAR TERM /THROUGH TONIGHT/... AS OF 400 AM EDT THURSDAY... STARTING THE DAY OFF WITH MOSTLY CLEAR SKIES...WITH THE ONLY CLOUD COVER OBSERVED ACROSS THE RIDGES OF SOUTHEAST WEST VIRGINIA. WHILE WIND SPEEDS HAVE DIMINISHED EAST OF THE BLUE RIDGE...STILL OBSERVING GUSTS IN PLACES ACROSS THE MOUNTAINS REACHING IN EXCESS OF 30 MPH. FOR TODAY...WIND SPEEDS WILL BEGIN TO INCREASE AGAIN BY AROUND 10 AM AS THE STRONGER WINDS JUST OFF THE SURFACE MIX DOWN TO THE GROUND. WHILE WIND SPEEDS WILL NOT BE A STRONG AS THOSE OBSERVED ON WEDNESDAY...STILL LOOKING FOR GUSTS TO REACH 35 MPH AT TIMES ACROSS THE MOUNTAINS...POSSIBLY 40 MPH IN SPOTS...WHILE GUSTS MAY EXCEED 25 MPH ACROSS THE PIEDMONT. NORTHWESTERLY WINDFLOW WILL MEAN A WIDE TEMPERATURE GRADIENT FOR AFTERNOON HIGHS...WITH LOW TO MID 50S EXPECTED FOR THE RIDGES FROM SOUTHEAST WEST VIRGINIA THROUGH THE HIGHLANDS OF NORTH CAROLINA. DOWNSLOPE WINDFLOW WILL HELP TEMPERATURES WARM FURTHER EAST...WHERE MID 60S ARE EXPECTED ACROSS THE SOUTHSIDE AND THE PIEDMONT OF NORTH CAROLINA. HIGH PRESSURE WILL CONTINUE TO BUILD IN FROM THE WEST TONIGHT... SETTLING ACROSS EASTERN KENTUCKY BY DAWN FRIDAY. EXPECT WIND SPEEDS TO DECREASE OVERNIGHT AS THE HIGH APPROACHES...ALLOWING THE DEEPER MOUNTAIN VALLEYS TO DECOUPLE...WHICH WILL MAKE FOR STRONG RADIATIONAL COOLING UNDER CLEAR SKIES. AS 850MB TEMPERATURES ARE EXPECTED TO RANGE FROM AROUND 0C OVER THE NORTH CAROLINA HIGHLANDS...TO -4C/-5C OVER THE ALLEGHANY HIGHLANDS BY FRIDAY MORNING...FEEL CONFIDENT THAT WE WILL HAVE POCKETS OF SUB FREEZING TEMPERATURES ALONG AND WEST OF THE BLUE RIDGE LATE TONIGHT. HAVE SEEN PLENTY OF GREEN UP ACROSS THE MOUNTAINS OVER THE PAST WEEK OR TWO...AND BELIEVE THAT SOME OF THE MORE SENSITIVE VEGETATION MAY BE AFFECTED BY THESE COLD TEMPERATURES. HAVE THEREFORE ISSUED A FREEZE WARNING FOR TONIGHT FOR AREAS ALONG AND WEST OF THE BLUE RIDGE. TEMPERATURES FURTHER EAST ARE EXPECTED TO REMAIN WARMER...AND EXPECT WIND SPEEDS TO BE A LITTLE TOO STRONG AND THE AIR TOO DRY FOR MORE THAN ISOLATED PATCHES OF FROST. TEMPERATURES SHOULD REBOUND QUICKLY AFTER 9 AM FRIDAY MORNING. && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... AS OF 400 AM EDT THURSDAY... DEEP UPPER LOW ANCHORED ACROSS THE EASTERN GREAT LAKES SLOWLY DRIFTING TOWARD THE NEW ENGLAND STATES WILL BE THE DOMINATE WEATHER FEATURE FOR OUR AREA THROUGH THE PERIOD. A SERIES OF EMBEDDED NORTHERN STREAM SHORT WAVES WILL CONTINUALLY REINFORCE THE UPPER LOW AND SLOW ITS EASTWARD PROGRESSION. THIS PATTERN WILL KEEP A PREVAILING NORTHWEST FLOW ACROSS THE REGION AND RESULTANT WELL BELOW NORMAL TEMPERATURES AS 850MB TEMPS HOVER NEAR 0C TO BELOW 0C AT TIMES...WITH A FEW EXCEPTIONS. MEANWHILE...A FAMILIAR WINTER LIKE PATTERN REMAINS IN PLACE TO THE SOUTH WITH A SPLIT FLOW AND AN ACTIVE SOUTHERN STREAM. FRIDAY WILL BEGIN WITH COLD HIGH PRESSURE DRIFTING ACROSS THE REGION FROM THE NORTHWEST WITH FREEZING TEMPERATURES LIKELY IN THE VALLEYS AND HIGHER ELEVATIONS WHERE 850MB TEMPS ARE WELL BELOW 0C EARLY FRI. A STRONG SHORT WAVE WILL BE MOVING RAPIDLY EASTWARD FROM THE CENTRAL U.S. WITH HIGH CLOUDS QUICKLY SPREADING INTO THE CWA BY EVENING. THE ANTECEDENT AIR MASS IS QUITE DRY...SO FELT THAT 00Z SAT WAS TOO QUICK TO BRING PRECIPITATION INTO THE WESTERN AREAS. BY DAYBREAK...HOWEVER...THE HIGHLY KINEMATIC SHORT WAVE WILL BRING WIDESPREAD RAIN SHOWERS INTO THE REGION. THE FAST MOVEMENT OF THIS SYSTEM AND LIMITED SFC-BASED MOISTURE...AT LEAST INITIALLY...SHOULD LIMIT RAINFALL AMOUNTS TO MOSTLY 1 INCH OR LESS...WITH THE HIGHEST AMOUNTS IN THE SOUTHWEST PART OF THE CWA. NORMALLY...THIS WOULD NOT BE A PROBLEM...BUT GIVEN THE RECENT HEAVY RAINFALL AND RIVER LEVELS STILL ABOVE NORMAL IN MOST AREAS...THIS WILL NEED TO BE WATCHED. AGAIN...THE CONCERN FOR FLOODING ISSUES IS QUITE MARGINAL AT THIS POINT. THE SUBSEQUENT MOVEMENT OF THIS SYSTEM WILL BE SOMEWHAT ABNORMAL AS THE NORTHERN/SOUTHERN STREAMS MERGE NEAR OUR SOUTHERN CWA BORDER AND THE SYSTEM BECOMES ABSORBED INTO THE SOUTHERN STREAM AND TRACKS EAST-SOUTHEAST THROUGH THE CWA INTO NORTHEAST NC. A SECONDARY AREA OF PRECIPITATION EVOLVES ON THE BACK SIDE OF THE EAST-SOUTHEASTWARD MOVING SFC LOW...BRINGING AN ADDITIONAL SURGE OF LIGHT RAIN INTO THE REGION SATURDAY NIGHT. THERE IS A SMALL THREAT OF THUNDERSTORMS IN FAR SOUTHWEST VA AND EXTREME SOUTHERN WV SATURDAY AFTERNOON/EVENING IN ADVANCE OF THE SFC LOW. AT THIS POINT...ANY SEVERE THREAT SHOULD REMAIN WEST OF OUR CWA...BUT CAPE/LIS/BROOKS-CRAVEN PARAMETERS SUGGEST AT LEAST SOME THREAT OF TSRA IN THIS AREA...LIKELY NOT UNDER THE INFLUENCE OF AN IN-SITU WEDGE THAT WILL EVOLVE FURTHER EAST CREATING A MORE STABLE ATMOSPHERE. TEMPERATURES WILL BE MOSTLY BELOW NORMAL THROUGH THE PERIOD...AND AS MENTIONED ABOVE...A WEAK IN-SITU WEDGE APPEARS EVIDENT IN THE RAIN EAST OF THE BLUE RIDGE SAT...HOLDING MAX TEMPS IN THE 50S. FOR SUNDAY...THE SFC LOW CONTINUES TO SLIDE EAST OFF THE VA/NC COAST WITH COOL HIGH PRESSURE BUILDING SOUTHWARD INTO THE REGION ON THE BACK SIDE OF THE PERSISTENT NORTHEAST U.S. LIGHT RAIN SHOWERS MAY PERSIST MUCH OF THE DAY SUNDAY AS THE SFC LOW/BAROCLINIC ZONE SLIDES ACROSS THE SOUTHERN PART OF THE CWA. THIS PRECIPITATION SHOULD BE LIGHT...BUT WILL SERVE...COMBINED WITH THE INCREASING NORTHWEST FLOW SFC/ALOFT...TO ENSURE WELL BELOW NORMAL TEMPERATURES. ALL PRECIPITATION SHOULD COME TO AN END BY SUNDAY NIGHT. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... AS OF 400 AM EDT THURSDAY... PERSISTENT PATTERN CONTINUES WITH AN UPPER LOW ACROSS THE NORTHEAST U.S. DRIFTING SLOWLY SOUTHWARD ALONG THE COAST...AND ANOTHER STRONG SHORT WAVE TRACKING EASTWARD FROM THE CENTRAL/SOUTHERN PLAINS. AS THE CENTRAL PLAINS UPPER LOW DRIFTS INTO THE INFLUENCE OF THE NORTHEAST U.S. UPPER LOW...DISCONTINUOUS RETROGRESSION TAKES PLACE WITH A DEEP UPPER LOW EVOLVING ACROSS THE TN VALLEY. MOST MODELS ARE IN GOOD AGREEMENT ON THIS PATTERN TAKING PLACE TOWARD MID-WEEK. GIVEN THE INCREASINGLY VERTICALLY STACKED NATURE OF THIS SYSTEM...IT WILL BE QUITE PERSISTENT AND EVENTUALLY WE COULD SEE AN ALMOST WINTERLIKE SCENARIO...ALBEIT WITHOUT THE SNOW...OF A COASTAL LOW DEVELOPING OFF THE SC/NC COAST WED-THU. RAINFALL COULD BE HEAVY AND FLOODING MAY BE A CONCERN...ESPECIALLY FOLLOWING QUICKLY ON THE HEELS OF THE WEEKEND SYSTEM. 7-DAY QPF FROM WPC SHOWS RAINFALL OF 2- 3 INCHES ACROSS THE SOUTHWEST PART OF THE CWA AND MUCH OF THIS WILL BE OCCURRING WITH THIS MID-WEEK SYSTEM. THE GOOD NEWS IS THAT THE SEVERE WEATHER THREAT SHOULD REMAIN LOW BECAUSE OF WELL BELOW NORMAL TEMPERATURES AND A STABLE AIR MASS. LITTLE TO NO THUNDER IS EXPECTED AS INSTABILITY IS NIL. IF THIS MID-WEEK SYSTEM WERE IN PLACE DURING JANUARY/FEBRUARY...WE WOULD BE TALKING ABOUT A LOT OF SNOW. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... AS OF 800 AM EDT THURSDAY... SURFACE HIGH PRESSURE WILL BUILD IN FROM THE WEST TODAY AND TONIGHT...WITH VERY DRY AIR ASSOCIATED WITH THE AIRMASS SUPPORTING VFR CONDITIONS THROUGH THE TAF PERIOD. THE PRESSURE GRADIENT FOR THE FORECAST AREA WILL REMAIN TIGHTENED THROUGH THE DAY AS THE HIGH BUILDS IN...WHICH WILL RESULT IN CONTINUED GUSTY NORTHWEST WINDS INTO LATE THIS EVENING...ALTHOUGH WIND SPEEDS WILL NOT BE AS STRONG AS THOSE OBSERVED ON WEDNESDAY. EXPECT GUSTS REACHING 30-35KTS ACROSS THE MOUNTAINS AND 25KTS EAST OF THE BLUE RIDGE THIS AFTERNOON. WIND SPEEDS WILL GRADUALLY DIMINISH THIS EVENING AND TONIGHT AS THE SURFACE HIGH BUILDS IN...EVENTUALLY PASSING OVERHEAD ON FRIDAY. DRY AIR ASSOCIATED WITH THE HIGH WILL ALLOW FOR CONTINUED VFR CONDITIONS...ALBEIT WITH INCREASING UPPER LEVEL CLOUDS AS ANOTHER DISTURBANCE APPROACHES FROM THE WEST. HIGH CONFIDENCE IN VFR CIGS/VSBYS THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN WIND SPD/HIGH CONFIDENCE IN WIND DIR THROUGH THE TAF VALID PERIOD. EXTENDED AVIATION DISCUSSION... OVERRUNNING CLOUDS WILL BUILD INTO THE AREA FRIDAY EVENING AHEAD OF A WARM FRONT FRIDAY NIGHT. BY SATURDAY...MOISTURE APPEARS DEEP ENOUGH TO ALLOW FOR PERIODS OF RAIN AND MVFR...WITH BEST FORCING ACROSS THE CAROLINAS. COMPLEX LOW PRESSURE TO THE WEST WILL THEN PUSH THROUGH THE REGION SATURDAY NIGHT INTO SUNDAY...BEFORE EXITING OFFSHORE SUNDAY NIGHT. THIS WILL LIKELY KEEP SUB-VFR CONDITIONS IN LOW CLOUDS AND LINGERING RAINFALL INTO SUNDAY NIGHT. FLYING CONDITIONS SHOULD START TO IMPROVE SOME BY MONDAY AS THE LOW PULLS FARTHER OFFSHORE AND WEAK HIGH PRESSURE BUILDS IN FROM THE NORTHWEST. HOWEVER CONTINUED CYCLONIC FLOW LIKELY TO KEEP MORE MVFR CIGS OVER THE MOUNTAINS WITH IMPROVEMENT TO VFR ACROSS THE EAST ON MONDAY. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT FRIDAY FOR VAZ007-009>020-022>024. NC...FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT FRIDAY FOR NCZ001-002-018. WV...FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT FRIDAY FOR WVZ042>044-507-508. && $$ SYNOPSIS...NF NEAR TERM...NF SHORT TERM...RAB LONG TERM...KK/RAB AVIATION...JH/NF/RAB

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